I love wooden kayaks

March 28, 2012

Building a Cedar Strip Stand Up Paddleboard

Katya has made a lot of progress on her stand up paddleboard. I am very happy to lend my expertise in this project and be able to document it. It will be good to work through the process and see how it’s done before I start to work on my own paddleboard. With the experience fresh in my mind and the notes I’ll be taking, the second time around should go much quicker.

Building a workbench

The first step was to built a 12 x 2 ft workbench. A lot of it was made out of salvaged lumber. It is basically a 1/2 in plywood surface secured with drywall screws to 2x2s around the circumference as well as a few crossbeams. The workbench was put on top of an 8 ft long folding table, and legs attached to support the ends. The workbench was leveled as much as possible side to side with shims placed under the legs. The assembly was still quite flexible and uneven along its length, and the entire garage surface sloped toward the entrance. This shouldn’t matter as long as it is stable though, because the frame’s central longitudinal (what the designers call the “spar”) will be mounted above the surface.

The plywood pieces of the frame (“ribs” and “spar”) have to be cut out of the wooden panels that come in the kit. The wood is thin, 1/8 in plywood. The instructions tell you to use a sharp chisel to cut the tabs holding the pieces in place and then sand the edges smooth. In my first post I complained about having to do this and wondered why the manufacturers don’t sell the kits with everything completely precut. But now I realize that it is very useful to have the surrounding scrap plywood on the panels. For instance, rib #2 broke in half while it was being cut out and I was able to make a copy out of the scrap plywood. The outside inch of the plywood panels is also used to make the sticks used to mount the frame to the workbench surface. These sticks are about 3/4 in wide by 6 to 3 inches long.

Broken rib #2

Copy of rib #2 made from scrap plywood

Mounting sticks made from scrap plywood

Gluing the spar

The spar is the 12 ft long center longitudinal piece that holds the ribs. Since the plywood panels are only 8 ft long, the spar comes in two pieces that have to be glued together with a butt joint. The kit comes with two gussets that are glued on each side of the joint. The instructions say to place a straight edge along the top edge of the spar pieces to ensure proper alignment and glue the gussets to each side of the spar at the joint, then place a weight over the joint and allow it to dry.

It sounds easy but during the first attempt the whole assembly slid out of alignment and dried that way. I think simply placing a big weight on a gluing joint is not a good idea. You can’t see the joint to check if it’s still in alignment while it is gluing when there’s a big weight on it.

In order to salvage the pieces, both gussets had to be carefully planed off the spars and all the dried glue (Gorilla Glue) scraped off. Two new gussets had to be made using plywood scraps from the 1/8th inch plywood panels. For the second attempt, clamps were used to secure the joint, and the joint was glued one gusset at a time. The ends of the spars had to be supported off the workbench because of the clamps. If the spar is not kept straight along its length while the joint is glued, it will be a little crooked at the joint.

This is the crappy joint that resulted from just using weights

The joint had to be carefully taken apart by planing off the gussets

The spar joint is reglued, first one side, then the other

Mounting the spar on the workbench

The spar is temporarily glued to the workbench with a hot glue, using the mounting sticks that were cut out of the plywood scrap. First a centerline is drawn on the workbench. (The instructions say to snap a chalk line, but we just drew a line along a piece of string tied along the center.)

This is one of the steps where it really helps to have two people. One person holds the mounting stick square against (not on) the centerline using a straight edge while the other person squirts a bead of hot glue along the bottom of the stick. The stick needs to be held in position for a minute until the glue cools. The mounting sticks are placed every 8-10 inches. It is important not to place a stick where a rib will be along the spar, because it will interfere with placement of the rib, so it helps to lay the spar along the centerline to know where the ribs will be. Because of the board’s rocker, the mounting sticks closer to the nose and tail will need to be taller (5-6 inches) than the ones in the middle (3 inches).

Once the mounting sticks are secure, sight along the line of sticks to make sure they are in alignment and square to the workbench surface. The spar is held up against one side of the sticks and secured with a few clamps or clothespins, starting at the center of the spar. It is important to have enough room between the spar and the workbench to be able to run the stretchy plastic wrap that will be used to clamp the strips to the deck, at least 1 inch. Trim off any sticks where the ends extend above the top of the spar.

Sight down the spar to make sure it is straight and square to the workbench surface. Once the spar is properly positioned, secure the spar to the mounting sticks by running a 1 inch bead of hot glue along the sides of each stick. Since the frame will eventually be removed from the workbench and all of the hot glue scraped off the spar, it is important to try to keep the hot glue to a minimum.

From the pictures, it should be obvious how thin and light this plywood is. It feels like you are making a model balsa wood airplane! The cedar strips will add a lot more strength and weight.
Next: Installing the ribs!